For the United States men's national team, it doesn't get much bigger than the upcoming group match against Portugal.

After finally shaking the curse of playing Ghana on the international stage, the Stars and Stripes now find themselves one win over Portugal from all but guaranteeing a spot in the knockout round. However, doing so won't be easy.

The United States face long odds as a 4-to-1 underdog according to Odds Shark.

With Germany pummelling the Portuguese 4-0 in the opening game of Group G, there's no doubt that the side will be looking to bounce back in a big way. Here's a look at some of the key factors that will determine the outcome of the match.

How Fit is Cristiano Ronaldo and Can the US Slow Him Down?

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Portugal may have looked like an inferior side against Germany, but it isn't as though they were at full strength. The Portuguese have been decimated by injuries and will be without Fabio Coentrao and Hugo Almeida against the United States, per Gerard Meagher of The Guardian.

But the injury that is hurting them the most may be a recurring issue with their key player's left knee. ESPNFCreports that Cristiano Ronaldo wore a brace on the troublesome knee in training leading up to the match. Which makes his condition a bit of a mystery.

Even if Ronaldo is only able to give Portugal a fraction of his usual brilliance on the pitch, he's going to be a handful for the American back line.

Former U.S. goalkeeper Kasey Keller told ESPNFC just how much focus and concentration it takes to properly mark Ronaldo throughout the match:

I think some of it is just complete concentration... If you're that right-sided back or midfielder, you have to understand that he wants to come inside and shoot. And if you can force him wide, then great. But you're almost forgetting any other responsibilities, and just completely concentrating on him, because if you don't he's going to be past you.

Against Ghana, the U.S. got away with allowing Ghana to routinely get the ball into the scoring third of the pitch. If they do that against Portugal, even a semi-fit Ronaldo will make them pay.

Can USMNT Replace Jozy Altidore?

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Somewhat lost in the euphoric aftermath of topping Ghana was the devastating loss of Jozy Altidore for the most important group play match. According to SportsCenter, the 24-year-old will not play against Portugal:

BREAKING NEWS: USMNT F Jozy Altidore will not play Sunday against Portugal due to strained left hamstring. pic.twitter.com/EDgVh6o4Fl

Playing alongside Clint Dempsey, Altidore has emerged as America's top dynamic scoring option. Replacing that kind of striking ability will be extremely difficult. As Albert Larcada of TruMedia illustrates, the United States attack took a sharp nosedive after Altidore was forced off the pitch against Ghana:

After Altidore's injury the US had two touches within 20 yards of Ghana's goal the rest of the match. One was a goal. pic.twitter.com/39XFjyBLx2

Of course, the United States still made do in that match. John Anthony Brooks stepped up as the unexpected hero with his match-winning goal. It's going to take that kind of effort from another relatively under-the-radar player to find goals without Altidore in this one.

Can the US Retain Possession?

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The US walked away from the Ghana match with the desired result. They'll take a win however they can get them at this stage. But the level of play they displayed won't continue to rack up wins against the likes of Portugal or Germany.

Although the final score read 2-1, it was Ghana who was constantly threatening offensively. As ESPN Stats & Info notes, the Germans did a much better job of keeping Ghana from the attacking third:

Ghana has 27 attacking third touches so far. They had 220 against USA. #GERvsGHA

Playing much cleaner and calculatedly will be pivotal for the Americans in this match. They will need to find a way to bring the possession numbers much closer to 50/50 than they did against the African nation.

If they are able to do that it's going to much easier to replace the goal production of Altidore while ensuring that Ronaldo still has a quiet World Cup appearance.

Then again as we learned in the side's World Cup opener, it isn't how many opportunities you create, but rather how well you capitalize on them. Even with the odds stacked against them, it's hard to deny that the Americans seem up for the challenge.